Butterfly is widely considered the toughest of all techniques. Much of this comes down to shoulder strength and timing.

Body position: Keep the body as close as possible to the surface of the water. The entire butterfly movement should be fluid and continuous - the hips act as a pivot point.

Head: Start with the arms forward and eyes looking slightly ahead. Press the head downwards as the hips move up. Tuck the chin into the chest when you are under the water, pushing the chin forward as you pull with the arms so that you are ready to breathe. Bring your eyes up slightly so that you are looking down but forward again. Your head should re-enter the water before your hands.

Breathing: Trying to breathe on every stroke can lead to hyperventilation. So, aim to breathe on every second stroke instead. Breathe at the point when your arms almost reach your thighs by pushing your chin forward so that your mouth comes out of the water. Breaths should be quick, not forceful.

Arms: Shoulder strength is essential. Keeping elbows slightly bent, the hands should be facing palms down and thumbs should enter the water first in front of your shoulders. Immediately begin to pull the arms towards the feet - not straight back, but with the elbows held high in a "hooking action". When the hands reach the thighs, lift the arms out of the water, throwing them forwards again.

Legs and feet: The kick should be strong but gentle as kicking too hard will interrupt the flowing action of the arms. Legs should be close together but not touching - you need to be able to turn your feet in slightly. Kick down with the legs as the hands enter the water and down again when they leave the water. A kick should end with the legs straight.